The present invention relates to methods for treating cells resistant to neoplastic agents. Although there are now a number of cytotoxic agents that help to produce a positive outcome in cancer patient therapy, many cancer cells develop resistance or are resistant to the neoplastic agents currently of choice for chemotherapeutic treatment. The development of drug resistance substantially compromises the efficacy of cancer therapy.
Multidrug resistance cells are one example of cells that are resistant to antineoplastic agents. In this case, the cells are resistant to more than one antineoplastic agent. Multidrug resistance is a well-defined phenomenon. Often cancer cells that become resistant to one class of anticancer drugs (i.e., Vinca alkaloids, anthracyclines, taxanes, including paclitaxel, epipodophyllotoxins, and the like) also demonstrate resistance to other anticancer drugs. Development of multidrug resistance creates a significant impediment in the generation of positive outcomes for many cancer patients. Multidrug resistant agents have a number of general features in common; they are generally lipophili, weakly basic molecules of greater than about 300 daltons or larger molecular weight. Multidrug resistant cells tend to accumulate anticancer drugs at a level lower than cells that are not multidrug resistant (Beck, W T, Adv. Enzym.o Regul 1984, 22:207). Accumulation of drug at lower levels has been shown in some models to be associated with an increase in activity or in the amount of a family of transmembrane channel proteins.
An example of transmembrane channel proteins that are capable of decreasing the intercellular concentration of anticancer drugs are the integral membrane proteins P-glycoproteins (Pgp, Endicott J A and Ling, V. Annu Rev. Biochem. 1989, 58:137). The proteins appear to bind to antineoplastic agents and release the agents into the extracellular milieu. Expression of the MDR1 cDNA, the DNA encoding Pgp, is sufficient to produce a multidrug resistance phenotype (Gros et al., Nature 1986, 323:728). These proteins are present in rodents and in man. Another protein associated with resistance to antineoplastic agents is the multidrug resistance-associated protein (MRP) (Grant C E et al., Cancer Res. 1994, 54:357). MRP has been shown to confer multidrug resistance to doxorubicin, vincristine, etoposide and colchicine. For a review of other multidrug resistance associated proteins see xe2x80x9cMechanismns of Drug Resistancexe2x80x9d by Beck and Dalton in Cancer: Principles and Practice of Oncology, p. 498-512, eds DeVita et al., Lippincott-Raven, N.Y., 1997.
Elevated levels of Pgp have been observed in a variety of cancers including, but not limited to, Acute Myelogenous Leukemia, Non-Hodgkin""s Lymphoma, multiple myeloma as well as in a variety of solid tumors including, but not limited to, cancers of the adrenal, colon, kidney, lung and breast (see Beck and Dalton, supra). Moreover, it is widely recognized that cancers having an origin in a variety of tissues and cells can develop multidrug resistance. Therefore, there is a need to identify and to use compounds that remain toxic to otherwise multidrug resistant cells.
In addition to multidrug resistance, there are other types of resistance to antineoplastic agents that have been observed. These include, for example, resistance to one or more antineoplastic agents as a result of a mutated protein. One example of resistance to antineoplastic agents results from mutations in microtubules or in mutations in tubulin dimers. Cellular resistance to taxanes such as paclitaxel, can be multifactorial. For example, cellular resistance to the taxane family has been associated in some instances with a mutation in the xcex2-tubulin subunit. Again, as in the case of multidrug resistant cells, there is a need for neoplastic agents that remain toxic to taxane-resistant cells.
The present invention relates to methods for treating cells with discodermolide. In one aspect, the invention relates to methods for treating cells with discodermolide in vivo.
In another aspect of this invention, the invention relates to a method for inhibiting the growth of multidrug resistant cells comprising the step of contacting at least one multidrug resistant cell with a growth-inhibiting amount of discodermolide. In one embodiment the multidrug resistant cell is resistant to taxanes, for example paclitaxel. In another embodiment the multidrug resistant cells are growth inhibited in vivo or in culture. Preferably the cell is from a mammmal and more preferably from a human.
In another aspect of this invention, the invention relates to a method for inhibiting the growth of a cancer cell comprising the steps of: contacting at least one cancer cell with a growth inhibiting amount of discodermolide wherein the cancer cell is resistant to at least one antineoplastic agent. In a preferred embodiment the cancer cell is selected from the group consisting of a leukemia cell, a lymphoma cell and a solid tumor cell. In one embodiment the cancer cell is a multidrug resistant cell. In another embodiment the cell comprises a mutation in xcex2-tubulin and in another embodiment, the cell over-produces glutathione. Preferably the cell is in a mammal.
The invention also relates to a method for promoting apoptosis in a multidrug resistant cell comprising the steps of contacting a multidrug resistant cell with discodermolide; and inducing apoptosis in the cell. In a preferred embodiment the multidrug resistant cell is resistant to paclitaxel. The cell can be a cell in culture or in vivo. Preferably the cell is from a mammal and more preferably from a human.
The invention further relates to a method for inhibiting the growth of cancer cells having a xcex2-tubulin mutation comprising the steps of; contacting at least one cancer cell with a growth inhibiting amount of discodermolide wherein the cell comprises a mutation in the protein xcex2-tubulin; and inhibiting cell division in the cell. In one embodiment the cell is resistant to paclitaxel or to another antineoplastic agent. Preferably growth inhibition occurs in vivo and more preferably growth inhibition occurs in a mammal, preferably a human. The invention also relates to a method for inhibiting growth of a tumor resistant to at least one antineoplastic agent comprising the step of: contacting a tumor with discodermolide wherein the tumor comprises cells resistant to at least one antineoplastic agent. In one embodiment the cells have a mutation in a xcex2-tubulin protein and in another embodiment the cells overproduce glutathione. In yet another embodiment, the cells are multidrug resistant. In a preferred embodiment, the at least one neoplastic agent is paclitaxel. In yet another embodiment the cells comprise raf-1 and wherein raf-1 is phosphorylated in the presence of discodermolide. Preferably the tumor is selected from the group of tumors consisting of lung, prostate, colon, breast, ovarian, kidney, brain, pancreatic esophageal, head and neck, gastric, and liver tumors.